In the beginning (taken here as prior to ~1980) libraries held five-year printed consolidated indices of molecules, organised by formula or name (Chemical abstracts). This could occupy about 2m of shelf space for each five years. And an equivalent set of printed volumes from the Beilstein collection. Those of us who needed to track down information about molecules prior to ~1980 spent many an afternoon (or indeed a whole day) in the libraries thumbing through these weighty volumes. Fast forward to the present, when (closed) commercial databases such as SciFinder, Reaxys and CCDC offer information online for around 100 million molecules (CAS indicates it has 89,506,154 today for example). These have been joined by many open databases (e.g. PubChem). All these sources of molecular information have their own way of accessing individual entries, and the wonderful program Jmol (nowadays JSmol) has several of these custom interfaces programmed in. Here I describe some work we have recently done on how one might generalise access to an individual molecule held in what is now called a digital data repository.
M.J. Harvey, N.J. Mason, and H.S. Rzepa, "Digital Data Repositories in Chemistry and Their Integration with Journals and Electronic Notebooks", Journal of Chemical Information and Modeling, vol. 54, pp. 2627-2635, 2014. http://dx.doi.org/10.1021/ci500302p